Should not be able to `path_open` absolute path

`path_open` an absolute path should error. This behavior is consistent amongst Wasmtime, WasmEdge, Wazero, WAMR.  Fixing this does not break clients using wasi-libc as it already strips the prefix by matching the path with the appropriate preopened directory.

WASI folks have also stated absolute path should not work at the raw WASI level. https://github.com/WebAssembly/WASI/issues/374

